Transient performance of parallel-flow and cross-flow direct transfer type heat exchangers with a step temperature change on the minimum capacity rate fluid stream
Parallel and cross-flow with both fluids unmixed, direct transfer type heat exchangers are modeled utilizing a thermal network consisting of nodes and resistors. A commercially available software package, Thermonet, calculates the transient outlet temperatures for a steadystate model introduced to a sudden change (step input) in inlet temperature of the Cmin fluid stream. Both models are validated against analytical solutions provided in literature. Solutions are verified to within a maximum percent mean difference of 4 % of analytical solutions for parallel-flow, and 8 % of analytical solutions for cross-flow heat exchangers. Tables are generated which provide new dimensionless transient outlet temperature effectiveness values for parallel and cross-flow with both fluids unmixed, heat exchangers. The parallel-flow temperature responses are presented in graphical form for the specific parameters: NTU equal to 0.5, 1.0, and 3.0; C* equal to 0.2, 0.6, and 1.0; R* equal to 0.5, 1.0, and 2.0; Cw* equal to 1.0, 10.0, and 1000.0; and td equal to 0.25, 1.0, and 4.0. The cross-flow temperature responses are presented in graphical form for the same parameters listed above except NTU is equal to 1.0. Discussion regarding the dimensionless parameters\u27 effects on the transient response of the heat exchanger is provided. The transient performance tables provide a quick reference for transient outlet temperature solutions required for practical industrial heat exchanger analysis
